The long term objectives of these studies are to understand the molecular mechanisms that regulate the usage of 3' terminus for the membrane (am) and secreted (as) forms of a mRNA and to determine the significance of this process in the generation of an IgA memory response. The association of a secretory IgA response with effective immunization against enteric pathogens argues that the goal in designing vaccines against the wide variety of bacterial and viral agents that gain access to the host via a mucosal route is the generation of an IgA memory response. The nature of cells that function as IgA memory cells is enigmatic. Phenotypically, functional IgA memory cells are resting, migA+ cells that make relatively low levels of a mRNA. A variety of studies demonstrate that IgA secreting cells are for the most part derived from cells that are fist induced to express migA. However, the migA expressing precursors make predominantly a mRNA. The consistent predominance of a mRNA could indicate that expression of migA is not obligatory step in the development of IgA secreting cells. Furthermore, the molecular mechanism that regulates choice of 3' terminus appears to be isotype specific aims of this proposal are to determine the properties of the a gene responsible for the predominance of a mRNA, the basis for differential regulation of 3'terminus usage by alpha and mu eta mRNA, and the relevance of IgA expression to the generation of IgA secreting cells. To accomplish these aims specific sequences in alpha will be altered and the effect of those alterations on the steady state levels of the two forms of alpha mRNA will be measured. In addition, trans-acting factors that bind to alpha and/or eta will be identified by gel mobility shift assays. Finally, gene targeting by homologous recombination will be used to create an insertional mutation in the membrane exon of alpha in a migM+, lymphoma that spontaneously switches to IgA expression/secretion. The effect of that mutation on the ability of the cells to mature to IgA secretion will be measured.